How much do you like courgettes? According to one Facebook page devoted to them, hundreds of people find them delightful enough to click the "like" button – even with dozens of other pages about courgettes to choose from.

There's just one problem: the liking was fake, done by a team of low-paid workers in Dhaka, Bangladesh, whose boss demanded just $15 per thousand "likes" at his "click farm". Workers punching the keys might be on a three-shift system, and be paid as little as $120 a year.

The ease with which a humble vegetable could win approval calls into question the basis on which many modern companies measure success online – through Facebook likes, YouTube video views and Twitter followers.

Channel 4's Dispatches programme will on Monday reveal the extent to which click farms risk eroding user confidence in what had looked like an objective measure of social online approval.

A Facebook page devoted to courgettes with hundreds of 'likes' Photograph: Facebook

The disclosures could hurt Facebook as it tries to persuade firms away from advertising on Google and to use its own targeted advertising, and to chase likes as a measure of approval.

That particular Facebook page on courgettes was set up by the programme makers to demonstrate how click farms can give web properties spurious popularity.

"There's a real desire amongst many companies to boost their profile on social media, and find other customers as well as a result," said Graham Cluley, an independent security consultant.

The importance of likes is considerable with consumers: 31% will check ratings and reviews, including likes and Twitter followers, before they choose to buy something, research suggests. That means click farms could play a significant role in potentially misleading consumers.

'Russell', the manager of the click farm identified by Dispatches None

Dispatches found one boss in Bangladesh who boasted of being "king of Facebook" for his ability to create accounts and then use them to create hundreds or thousands of fake likes.

Click farms have become a growing challenge for companies which rely on social media measurements – meant to indicate approval by real users – to estimate the popularity of their products.

For the workers, though, it is miserable work, sitting at screens in dingy rooms facing a blank wall, with windows covered by bars, and sometimes working through the night. For that, they could have to generate 1,000 likes or follow 1,000 people on Twitter to earn a single US dollar.

Sam DeSilva, a lawyer specialising in IT and outsourcing law at Manches LLP in Oxford, says of the fake clicks: "Potentially, a number of laws are being breached – the consumer protection and unfair trading regulations. Effectively it's misleading the individual consumers."

Dispatches discovered an online casino which had sublicensed the Monopoly brand from its owner, the games company Hasbro, and to which fake likes had been added on its Facebook page.

When contacted, Hasbro contacted Facebook and the page was taken down. In a statement, Hasbro said it was "appalled to hear of what had occurred" and was unaware of the page.

Dhaka-registered Shareyt.com, meanwhile, claims to act as a middleman to connect companies seeking to boost their profile on Facebook, Twitter, Google +1, LinkedIn and YouTube.

"We made it as simple as mouse-clicking," the front page of the site says, claiming that it is "a crowd-sourcing platform to help you improve social media presence and search engine ranking FREE".

It adds: "Whenever and wherever you need massive workforce to complete petty tasks, call for Shareyt and get it done like magic! You can't imagine the potentials [sic] until you explore!" It claims to have generated 1.4m Facebook likes and to have 83,000 registered users.

The implication is that the site "crowdsources" clicks – that lots of people around the world mutually help each other to promote each others' work.

But Sharaf al-Nomani, Shareyt's owner, told Dispatches in an undercover meeting that "around 30% or 40% of the clicks will come from Bangladesh" – which implies about 25,000 people in Dhaka using computers laboriously and repetitively for hours on end to boost the visibility of specific products to order.

Some companies have used shareyt.com in the course of standard marketing.

Although it has so far only been released in South Korea, Facebook data suggests the city of Dhaka is the source of the third-largest number of likes. (The Egyptian capital, Cairo, is presently the source of the highest number.)

Tessa Hartmann of Billi Productions, which made the film, said they had been promoting it since 2006, and paid £271.40 to advertise it on shareyt.com in August 2012 for six months as a "very small" part of their marketing campaign. At the time, she says, it already had 40,000 Facebook likes. Her company stopped using the site in February.

A link also appeared on shareyt.com to Coca-Cola's 2010 Super Bowl advertisement "Hard Times", showing the Simpsons' Mr Burns learning to get by on less (but with Coke).

The video's presence on the site is likely to have helped its nearly 6m views. Coke said in a statement that it "did not approve of fake fans"; the video was made private soon afterwards.

Shareyt.com has now seen Facebook and Twitter prevent links to the site being posted on their networks. Twitter bans "fake followers" or the buying of followers.

Faked internet use has been a bugbear of the burgeoning advertising industry ever since the web went commercial in the mid-1990s and the first banner ad was rolled out in 1996.

The rise of advertising networks and "pay-per-click" advertising – where an advertiser pays the network when someone clicks on an advert, whether or not it leads to a sale – also saw a rise in faked clicks which benefited unscrupulous networks.

And it is still a problem. In February, Microsoft and Symantec shut down a "botnet" of up to 1.8m PCs that were being used to create an average of 3m clicks per day, raking in $1m per year since 2009.

But click farms exploit a different sort of computing power altogether: the rise of cheap labour paired with low-cost connectivity to the internet.

"Russell", the manager of the click farm identified by Dispatches, said some of the methods he used were legitimate; he blamed those who commissioned the work if it was seen as immoral.

In a statement, Facebook responded: "A like that doesn't come from someone truly interested in connecting with the brand benefits no one. If you run a Facebook page and someone offers you a boost in your fan count in return for money, our advice is to walk away – not least because it is against our rules and there is a good chance those likes will be deleted by our automatic systems.

"We investigate and monitor "like-vendors" and if we find that they are selling fake likes, or generating conversations from fake profiles, we will quickly block them from our platform."

Dispatches: Celebs, Brands and Fake Fans on Channel 4 at 8pm on Monday

• This article was amended on 5 August 2013 to add a response from Facebook that was received after publication.